Upon exposure to unusual fluid mechanical conditions or contact with non-biological surfaces, erythrocytes can undergo injury. This injury may be sufficient to lead directly to hemolysis. More common and probably more important clinically is the possibility of sublethal damage, resulting in altered red cell deformability, changes in membrane permeability, and erythocyte metabolism. In vivo, this can lead to seguestration of damaged cells by the spleen and liver - causing a shortened life span. The objective of this proposal is to assess quantitatively changes in red cell biophysical and biochemical properties caused by precisely known levels of shear stress and foreign surface exposure. These levels will be much lower than those necessary to cause large scale hemolysis, and more representative of the fluid mechanical experience an erythrocyte experiences upon passage through a hemodialysis coil or a heart-lung bypass. We will treat this trauma induced deformability defect as an in vitro model system to examine the complex interrelationships between red cell morphology, metabolism and deformability. Thus, the results should be of importance to a wide range of clinical abnormalities which involve changes in biophysical and biochemical state of the erythrocyte, leading to altered cell rheology in the microcirculation.